## The photon content of the proton in the CT18 global analysis

Keping Xie, T. J. Hobbs, Tie-Jiun Hou, Carl Schmidt, Mengshi Yan, C. -P. Yuan

SciPost Phys. Proc. 8, 074 (2022) · published 12 July 2022

- doi: 10.21468/SciPostPhysProc.8.074
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### Abstract

Recently, two photon PDF sets based on implementations of the LUX ansatz into the CT18 global analysis were released. In CT18lux, the photon PDF is calculated directly using the LUX master formula for all scales, $\mu$. In an alternative realization, CT18qed, the photon PDF is initialized at the starting scale, $\mu_0$, using the LUX formulation and evolved to higher scales $\mu(>\mu_0)$ with a combined QED+QCD kernel at $\mathcal{O}(\alpha),~\mathcal{O}(\alpha\alpha_s)$ and $\mathcal{O}(\alpha^2)$. In the small-$x$ region, the photon PDF uncertainty is mainly induced by the quark and gluon PDFs, through the perturbative DIS structure functions. In comparison, the large-$x$ photon uncertainty comes from various low-energy, nonperturbative contributions, including variations of the inelastic structure functions in the resonance and continuum regions, higher-twist and target-mass corrections, and elastic electromagnetic form factors of the proton. We take the production of doubly-charged Higgs pairs, $(H^{++}H^{--})$, as an example of scenarios beyond the Standard Model to illustrate the phenomenological implications of these photon PDFs at the LHC.

### Authors / Affiliations: mappings to Contributors and Organizations

See all Organizations.-
^{1}Keping Xie, -
^{2}^{3}^{4}^{5}Timothy Hobbs, -
^{6}Tie-Jiun Hou, -
^{7}Carl Schmidt, -
^{8}Mengshi Yan, -
^{7}Chien-Peng Yuan

^{1}University of Pittsburgh^{2}Thomas Jefferson National Accelerator Facility [JLAB]^{3}Fermi National Accelerator Laboratory [Fermilab]^{4}Southern Methodist University [SMU]^{5}Illinois Institute of Technology [IIT]^{6}Northeastern University [NEU]^{7}Michigan State University [MSU]^{8}北京大学 / Peking University [PKU]